The present invention relates to a light-beam scanning apparatus and an image forming apparatus, both for use in digital copy machines, laser printers or the like in which the photosensitive drum is scanned with a laser beam to form a latent image on the photosensitive drum.
To increase the image-forming speed, digital copy machines and the like have been developed, which comprise a light beam scan apparatus of multi-beam type. The light beam scan apparatus generates a plurality of light beams and scans a plurality of lines with these light beams at the same time.
Digital copy machines comprising an optical section such as a light beam scan apparatus are known. In each of the copy machines, the positions of the light beams are controlled in two modes to form high-quality images. First, the positions where the light beams are applied are controlled in the scanning direction (i.e., control of beam positions in the main scanning direction). Second, the positions where the light beams pass are controlled (i.e., control of beam positions in the sub-scanning direction).
In the conventional beam-position sensor, however, two timing sensors that detect the start and end, respectively, are identical in the sub-scanning direction. Therefore, they may malfunction at the boundary between their effective detection region and non-effective detection region. Consequently, the light beams may not be controlled to pass at desired positions. Further, the beam-position sensor cannot have the desired sensitivity, because the components of its beam-detecting section have characteristics different from the design values. (The photodiode has sensitivity different from the designed value, the operational amplifier has an offset-voltage and —resistance different from the design values, and the capacitor has a capacitance difference form the designed value.)